The present invention relates to a motor having an index detection mechanism used for a disc apparatus and a disc apparatus using such a motor, and more particularly to a motor having an index detection mechanism comprising an index magnet and a hall device for detecting an index of a rotor of the motor and a disc apparatus using such a motor.
Conventionally, a radial gap type motor is known, which motor is a spindle motor used for rotationally driving a disc for a disc apparatus. This type of motor comprises a stator including coils arranged on a base plate and a rotor including magnets mounted on a rotor case. This construction requires each coil having a large cross section to have a number of turns sufficient to generate a predetermined magnetic flux, and thus the motor has to be made quite thick. Accordingly, there is a limit to how far the thickness of a disc apparatus using a radial gap type motor can be minimized.
Recently, an axial gap type motor, in which coils and magnets are arranged in the direction of an axis of a spindle shaft, has been used. In this type of motor, since a space between respectively opposing coils and a magnet extends in a radial direction of the motor, such a space can be wide. This construction allows the thickness of this axial gap type motor to be less than that of a radial gap type motor. Therefore, the thickness of a disc apparatus using the axial type motor can be minimized more than can the thickness of a disc apparatus using the radial gap type motor.
However, a technique for minimizing the thickness of the coils in a radial gap type motor has been developed and thus a radial gap type motor as thin as the axial type motor has become available for production.
Due to this minimization of the thickness of a disc apparatus, a distance between a magnet of an index detection mechanism and a magnetic head for a disc apparatus, nay now be minimized.
FIG. 1 is a side view of an example of an index detection mechanism in a disc apparatus using a conventional motor. Reference numeral 1 indicates a spindle motor, 6 a spindle shaft and 4 a base plate having parts for the motor provided thereon. A conventional index detection mechanism 10 comprises an index magnet 3 provided on a rotor case 2 and a hall device 5 mounted on a base plate 4. The index magnet 3 is provided to a part of a side face of an outer periphery of the rotor case 2, which case is a rotational part of the spindle motor 1. A Hall device 5 is mounted in a position separate from opposite to the index magnet 3 on the base plate 4, which plate is provided with a stationary part of the spindle motor 1. More specifically, the Hall device 5 is mounted in a position slightly apart from the outer periphery of the rotor case 2 in the radial direction thereof.
The index magnet 3 rotates with each rotation of the rotor case 2 and passes a very short distance from the Hall device 5, every rotation of the rotor case. At the moment of perigee between the Hall device 5 and the index magnet 3, a magnetic flux generated by the index magnet 3 goes across the Hall device 5 and a resulting electric signal is output from the Hall device 5. The position where the electric signal is output becomes an index point. A disc position of a disc cartridge attached to the rotor case 2, placed against the rotor case 2, is determined by the spindle shaft 6 and a drive pin 9. This allows a disc to always be attached to the same position on the rotor case 2. By the above mentioned construction, a signal for a disc index can be obtained.
According to the arrangement of the component parts of the above index detection mechanism 10, the index magnet 3 is positioned close to a magnetic head of a disc apparatus with miniaturization of the thickness of the disc apparatus. This causes a leaking magnetic flux A to go through the heads 7,8 and results in a problem in that the leaking magnetic flux A affects the recording and playing function of the heads 7,8.